With the increasing number of premature infants surviving to reach BPD units, one wondered how long the system could survive the extremely high cost of long term care (about $700,000/year/patient in the unit). In response to such costs, patients are now being transferred to extended care facilities very early in the course of their disease, creating significant compromise to the effectiveness of their management. Both environments should welcome noninvasive instrumentation providing precise monitoring of physiologic respiratory variables at lesser cost. Such a tool would enable more effective respiratory management, even by less sophisticated care givers. This could facilitate moving patients to home care much earlier. However, because of the unavailability of noninvasive monitoring (PaCO2 in particular), and the lack of reasonable access to arterial blood, these patients are presently managed on ventilators without access to the guidance of PaCO2 (and other cardiopulmonary parameters). Invasive monitoring of these variables is usually available to hospitalized adults having comparable pulmonary dysfunction, at some risk and considerable cost. This proposal addresses the development of a noninvasive PaCO2, Pv-O2, and cardiac output (C.O.) monitor designed to overcome both physiological and technical problems of current systems which prevent their effective utilization for monitoring of patients such as those described. The proposed technique utilizes an inert gas technique applied to the lung form monitoring the V/Q distribution of gas exchanging units to provide data for relating continuously expired CO2 (P2CO2) measurements to PaCO2 values, (as well as measurements of Pv-CO2 and Pv-O2). A key to practical implementation of the method for extended home care and home use is the adaptation of small, economical sensors-newly developed for environmental uses-to serve as the system's gas analyzer. The method imposes to additional incumbrance for patients on ventilators. Additional applications include infants in intensive care units for whom the risks of monitoring by standard techniques are unacceptably high.